Exemplary embodiments of the present invention relate to a photomask for use in a semiconductor fabrication, and more particularly, to a method and system of fabricating an alternating phase shift mask.
As the integration density of semiconductor devices has recently increased, patterns constituting semiconductor devices have also become fine. With such a trend, when fine patterns are formed, phase shift masks (PSM) are widely used as one of resolution enhancement technologies. One of such phase shift masks is an alternating phase shift mask. The alternating phase shift mask has a structure in which phase shift patterns are disposed on a binary mask. In a phase shift region where the phase shift patterns are disposed, an electric field is shifted by 180 degrees and thus adjacent patterns do not interfere with each other. Accordingly, small patterns can be patterned at a high contrast, as compared to the binary mask.
FIG. 1 is a cross-sectional view illustrating an example of an alternating phase shift mask. Referring to FIG. 1, the alternating phase shift mask includes light blocking patterns 120 on a transparent substrate 110 such as a quartz substrate. The light blocking patterns 120 may be formed using a chromium (Cr) film. A trench etched by a predetermined depth d is disposed in a portion of the transparent substrate 110 exposed by the light blocking patterns 120. The trench serves as a phase shift pattern 112.
In fabricating such an alternating phase shift mask, it is important to precisely control the depth d of the trench-shaped phase shift pattern 112. This is because the depth d of the trench-shaped phase shift pattern 112 determines a phase difference in the phase shift region. Since it is not easy to detect an etch end point due to the structure of the phase shift mask, an etch process for forming the phase shift pattern 112 is performed by calculating an etch rate and determining a time necessary to etch the substrate to a desired depth. However, such a method does not consider parameters based on etch environments, such as a pattern density and an etching apparatus. Due to such parameters, the phase shift pattern 112 may not be formed at a desired depth. Consequently, a phase difference deviation occurs in the phase shift region, causing pattern failure during pattern transfer.